This invention is directed generally to filter systems for removing particulate matter from fluid streams in spray coating operations, and more particularly to a novel filter apparatus. The present invention provides an inexpensive and easily constructed filter made of readily available materials which offers extended filter life due to its shape and arrangement. It also provides a means of arranging the filters in spraying operations which results in maximum filter life and minimum down time.
Many manufactured objects require a coating with a protective or decorative coat of paint or some other protective material before they can be used. This coating may be applied by brushing, rolling, dipping, or spraying. The present invention is concerned with the spray application of a coating.
The spray application of a coating may be done by three general methods: air atomization, wherein coating particles ride on a fluid stream from the spray gun to the object being coated; airless atomization, utilizing hydraulic pressure to atomize and propel the coating; and electrostatic spraying, utilizing air or airless atomization and deposition of the coating by electrical attraction between the coating particles and the object being coated.
When spray coating by any of these methods, an environment is created that is hazardous to the person performing the work, the operation itself, and the atmosphere as a whole. For that reason, present day spray booths are designed to rapidly and thoroughly remove both volatile fumes (which are present when an operation such as spray painting takes place, which utilizes particulate dissolved in a liquid solvent) and particulate overspray from work areas. The spray booths create a safe environment for workers, minimizes pollution of the atmosphere, and maximizes the efficiency of the coating operation by removing overspray, thereby preventing finish-marring consequences of semi-dry coating particles settling on already coated surfaces.
Typically, a cross-draft spray booth consists of an enclosure within which the actual coating will take place. The enclosure has an air inlet and an exhaust. By drawing air into the enclosure and subsequently exhausting the air, an air flow is created that carries both fumes and overspray from the booth. The air flow passes through filters before exiting to remove solid particulate. The filters are located in the same enclosure where the coating takes place. The air is then exhausted to the atmosphere.
The industry generally uses planar filter arrangements in a cross-draft spray booth. In this system, a fluid stream is drawn through a planar sheet of filtering material that is stretched across the width and height of the open face of the booth. The filter bank actually creates an exhaust chamber, from which an exhaust fan draws air.
The advantage of this type of system is that the filtering materials used are cheap and are generally thrown away when dirty. When one planar sheet of filter material becomes clogged to the point that the exhaust fan cannot function properly, it is replaced with a new sheet, which is obtained from sheets or rolls of filter material which are readily available. Further, cross-draft spray booths can be used for all types of coating operations, including wet operations which utilize particulate dissolved in a solvent, and dry operations, which utilize particulate mixed with air.
The primary disadvantage of the conventional cross-draft booth is that as air is passed through the filter bank, solid particulate gradually builds up. Eventually the build up prevents the exhaust fan from operating properly. At this point, production must stop while the dirty filters are removed and replaced. The frequency of the shut down time is directly related to the volume of particulate that the filters are able to hold before becoming so clogged that the exhaust fan can no longer draw air effectively.
It is an object of this invention to provide a novel filter arrangement which extends filter life, thereby minimizing the frequency of down time and increasing productivity.
It is a further object of this invention to utilize readily available and inexpensive filter media currently used in cross-draft type spray booths.